1. Field of the Invention
The present invention relates to a field emission system and a method for improving its vacuum, and more particularly, to a field emission system employing surface-unsaturated nanomaterial as getter material.
2. Description of Related Art
In field emission display (FED) devices, each pixel contains several hundreds to thousands of micro-tip emitters or cabon nanotubes (CNTs) formed on a back plate of the field emission display device to serve as electron emission sources, and a phosphor layer emitting light by way of being bombarded by electrons from the electron emission sources is formed on a front plate of the field emission display device. A gap between the front plate and the back plate of the field emission display device is usually about 200 μm to several millimeters (mms). The display must be maintained in a high vacuum level so that electrons move without energy loss.
FIG. 1 is a schematic cross-sectional view of a conventional field emission display device. The conventional field emission display device includes a front plate 100 and a back plate 110 that are spaced from one another by a gap. An anode array 101 and a cathode array 111 are respectively formed on opposite inner surfaces of the front plate 100 and the back plate 110. A gate insulating layer 112, in which holes 112a are formed, is disposed on the cathode array 111, and the holes 112a make partial portions of the cathode wires of the cathode array 111 being exposed. A plurality of gate electrodes 113 corresponding to the holes 112a are formed on the gate insulating layer 112. A plurality of carbon nanotubes 114 grow on the exposed partial portion of the cathode wire in each of the holes 112a is served as field emission source, and the carbon nanotubes 114 in each of the holes 112a corresponds to one pixel unit. A phosphor layer 102 corresponding to the carbon nanotubes 114 are formed on the lower portion of the anode array 101, and a black matrix 103 for improving contrast and color purity of the field emission display device is formed in the phosphor layer 102 and inter-disposed with pixel units. An exhausting channel 115 passes through one side of the back plate 110 for exhausting residual gas, and a sealing cap 116 is used for sealing the outlet of the exhausting channel 115. A gas channel 117 passes through the other side of the back plate 110, and a getter container 118 including a getter 119 for absorbing residual gases inside the panels is connected to one end of the gas channel 117 and protruded outwardly from the back plate 110.
In the field emission process, if there are residual gases in the vacuum field emission system, these residual gas molecules would interact with field emission electrons and becomes ionized. The ionized species are accelerated toward the cathode under the application of electric field, and finally bombarding onto the surface of emitters with a certain quantity of energy. It is so-called ion bombardment. Under the influence of ion bombardment, the shape of the emitter tip is gradually deteriorated, and the distribution of electric field is affected. Finally, the field emission current decreases and even disappear. The field emission process may not be performed in an absolute vacuum level. Therefore, the decrease of the field emission performance caused by ion bombardment is almost unavoidable. However, ion bombardment strength is correlated with the vacuum level of the system very much. The higher the vacuum level is, the less the residual gas is, and ion bombardment becomes weaker. As shown in FIG. 1, conventionally the getter 119 is used to absorb most of gas molecules and ions inside the panel to decrease the ion bombardment effect. Because the getter 119 absorbs gas through the gas channel 117 which is narrow and has a quite large gas-flow resistance, the getter 119 would not effectively absorb gas inside the panel. In other words, it is difficult for the getter 119 to absorb the residual gas far away from the gas channel 117. The vacuum level of the field emission display device is limited.
Accordingly, it is an intention to provide an improved getter device applicable in the field emission display device to alleviate the drawbacks of the conventional field emission display device.